This invention relates generally to the removal of gaseous bubbles entrained in solution and, more particularly, to eliminating bubbles from a solution such as a photographic emulsion or dispersion using ultrasonic transducers, which create acoustic waves within the solution.
There are a variety of emulsions, suspensions, pastes and high viscosity liquids used in a manufacture of or which become part of a variety of products in the chemical, pharmaceutical, food product, and photographic industries. These emulsions, suspensions, pastes and high viscosity liquids often contain entrained air or gases present in the form of small bubbles. Often this air or gas, particularly in the case of entrained bubbles, is detrimental to the final product being produced. For example, in the case of photographic emulsions containing bubbles, the quality of the films or photographic papers produced is greatly impaired, giving rise to coated defects making the photographic materials unusable.
The use of ultrasonics in the debubbling or deaeration of liquids is widespread. For example, U.S. Pat. No. 3,239,998 to Carter et al. uses ultrasonics to debubble multiple liquids simultaneously, while U.S. Pat. No. 5,834,625 to Kraus Jr. et al. describes removing air from a discrete sample of liquid using ultrasonics. Other, more simplistic but similar techniques employing a vessel and ultrasonic transducer(s) propose operation under a slight vacuum pressure, allowing trapped gas to be removed from a single solution. Such techniques are taught in U.S. Pat. No. 3,904,392 to Van Ingen et al., U.S. Pat. No. 4,070,167 to Barbee et al., and U.S. Pat. No. 5,372,634 to Monahan. The vacuum technique, while apparently quite popular, does not appear to assist greatly in bubble removal, and its effectiveness is significantly reduced when dealing with more viscous solutions.
An apparatus which is typically used in the photographic industry for de-bubbling photographic emulsions is an end cap round ultrasonic bubble eliminator, typically referred to as an ECR. The ECR includes a transducer for assembly (hereinafter referred to as a xe2x80x9cTHAxe2x80x9d) which is an electromechanical device which converts electrical vibration to mechanical vibration. One particular ECR with its component THA is taught in U.S. Pat. No. 5,373,212 to Beau. In the operation of an ECR, an alternating voltage is applied to a ceramic disc of the THA which, as a result, generates mechanical vibration. This mechanical vibration assists in the de-bubbling of the photographic emulsions flowing through the ECR.
U.S. Pat. No. 4,070,167 to Barbee et al. describes an apparatus with a single ultrasonic transducer placed in the vertical position beneath a horizontal tubular vessel. The apparatus has a fairly complicated recycle stage which includes a further compartment with ultrasonics, typically operated under positive pressure. This setup is quite cumbersome, and there are inherent difficulties both in operation and cleanability of the apparatus in such an arrangement.
In devices which use ultrasonics for debubbling, the acoustic forces emanating from the transducers aid in the separation of gaseous bubbles from solution, as they assist the upward buoyancy force in opposing the downward drag force of the bubbles in solution. This phenomenon has been commonly used in the debubbling of flowing solutions (e.g. U.S. Pat. No. 3,904,392 to Van Ingen et al., U.S. Pat. No. 4,070,167 to Barbee et al., U.S. Pat. No. 5,373,212 to Beau, U.S. Pat. No. 4,398,925 to Trinh et al.).
Prior art ultrasonic debubbling devices are generally unitary vessels with vertically oriented ultrasonic transducers residing in vertically oriented wells. In this manner, the flow of liquid into the vertically oriented wells is generally vertically downward against the vertically upwardly directed acoustic waves emanating from the transducer. Bubbles are carried vertically upward through the well and the main vessel. As such, the upward flow of bubbles is resisted by the downward flow of the liquid.
It is therefore an object of the present invention to provide an ultrasonic debubbling apparatus with improved debubbling capacity.
It is a further object of the present invention to provide a bubble flow path which causes the bubbles to accumulate along a well wall.
Another object of the present invention is to provide a bubble flow path which allows the discrete bubbles to coalesce to thereby enhancing bubble removal.
Yet another object of the present invention is to provide an apparatus for bubble removal where the transducer horn assembly well and, therefore, the orientation of the ultrasonic transducer may be reoriented thereby allowing the flow path of bubbles through the wells to be angled depending on the flow rate and viscosity of the liquid.
Still another object of the present invention is to provide an apparatus wherein the number of transducer horn assembly wells and the number of ultrasonic transducers is adjustable.
Briefly stated, the foregoing and numerous other features, objects and advantages of the present invention will become readily apparent upon a review of the detailed description, claims and drawings set forth herein. These features, objects and advantages are accomplished by removing bubbles from solution by passing it through a horizontal tubular vessel with ultrasonic transducers situated in wells extending beneath the main tubular vessel. The vessel is typically operated at atmospheric conditions, and the solution is set to a specific level within the vessel, creating an air/liquid interface. The number of transducers could typically be one, two or more. The wells in which the transducers reside are oriented so as to be acutely angled from vertical. Preferably, the wells in which the transducers reside are oriented at an angle in the range of from about 30xc2x0 to about 45xc2x0 from vertical. The optimum angle will depend on viscosity of the liquid being debubbled as well as the flow rate of the liquid. As such, the angle for any liquid being debubbled can be determined empirically. With an angled well, the buoyant force, fluid drag force, and acoustic wave force exerted on an individual bubble in the well yield a resultant force that causes the bubble to travel to the upper side wall of the well containing the transducer, where bubble accumulation takes place. The accumulated air gradually rises along the inner wall of the vessel to the air/liquid interface. As this passage of air removal has been concentrated to the walls of the vessel, it is largely unaffected by the incoming bubble containing liquid, and hence removal efficiency is greatly improved. The need for a recycle stream, as necessitated by prior art debubbling apparatus (U.S. Pat. No. 4,070,167 to Barbee et al.) is eliminated, thereby simplifying the apparatus and operation thereof significantly. In the more common arrangement of the horns situated in the vertical plane, the passage of air removal is directly opposed by the incoming bubbly fluid, creating an upper limit to the degree of deaeration possible in this configuration.
The present invention is primarily intended for removing bubbles from a flowing solution, although it is likely that discrete samples of fluid may also be treated using this invention.